The present invention relates to an angular rate sensor.
FIG. 4 shows an example of angular rate sensors that have been proposed in the past. In FIG. 4, a support pin 101 made of metal is press-fitted perpendicularly and secured in a weight plate (not shown in the figure), and one end of another support pin 102 made of metal is press-fitted and secured in the support pin 101 in an orthogonal direction to it. A block 103 also made of metal is fixed at the other end of the support pin 102 by soldering. Vibration plates 104 and 105 are fixed at both ends of the metal block 103. A piezoelectric element 106 is bonded on the vibration plate 104 to constitute a vibration exciter 150, and another piezoelectric element 107 is bonded on the vibration plate 105 to constitute a means 160 for detecting a level of vibrations. A tip of the vibration plate 104 is extended in a manner to form a right angle with the piezoelectric element 106 to become a detecting plate 108. A tip of the vibration plate 105 is also extended in the same manner to form a right angle with the piezoelectric element 107 to become another detecting plate 109. Piezoelectric elements 110 and 111 are bonded on the detecting plates 108 and 109 respectively, to constitute detecting means 170 and 180 for detecting a Coriolis"" force generated in proportion to an angular rate. All of the above complete an element unit 112 of a tuning-fork type angular rate sensor.
A structure of FIG. 4 further comprises;
(a) a current amplifier 120 for amplifying an output signal from the piezoelectric element 107 provided on the vibration plate 105 to detect a level of vibrations of the vibration plate 105, which vibrates in a tuning-fork phenomenon in concert with vibrations of the vibration plate 104;
(b) a full-wave rectifier circuit 122 for producing a D.C. voltage by rectifying an output signal of a band-pass filter (hereinafter referred to as xe2x80x9cBPFxe2x80x9d) 121, wherein an output signal of the current amplifier 120 is input;
(c) an automatic gain control circuit (hereinafter referred to as xe2x80x9cAGCxe2x80x9d) 123 whose amplification factor for the output signal of the BPF 121 varies according to a magnitude of an output signal of the full-wave rectifier circuit 122;
(d) a driver 124 for driving the piezoelectric element 106 bonded on the vibration plate 104 in accordance with a magnitude of an output signal of the AGC 123;
(e) a charge amplifier 125 for inputting and amplifying output signals of the piezoelectric elements 110 and 111, which detect a Coriolis"" force generated in proportion to an angular rate;
(f) a synchronous detection circuit 127 for detecting an output signal of a BPF 126, wherein an output signal of the charge amplifier 125 is input;
(g) a sensor output terminal 129 for outputting an output signal of a low-pass filter (hereinafter referred to as xe2x80x9cLPFxe2x80x9d) 128, wherein an output signal of the synchronous detection circuit 127 is input;
(h) a determination circuit 130 for inputting the output signal (an amplitude of signal at a point xe2x80x9cAxe2x80x9d) of the full-wave rectifier circuit 122 and the output signal (an amplitude of signal at a point xe2x80x9cBxe2x80x9d) after amplified by the charge amplifier 125, and determining an abnormality; and
(i) an abnormality diagnosis terminal 131 for communicating an abnormality to an outside from the determination circuit 130, when it determines the abnormality. A reference numeral 132 represents a power supply connection terminal, and a reference numeral 133 represents a grounding terminal. The elements described above constitute a driving circuit 134.
The angular rate sensor is completed by having the above element unit 112 of a tuning-fork type angular rate sensor and the driving circuit 134.
In addition, a voltage E is supplied from a power source 135 to the power supply connection terminal 132 of the driving circuit 134. A load resistor 136 is connected to the sensor output terminal 129, and an output signal C is supplied toward a controller side (not shown in the figure). In the like manner, a load resistor 137 is connected to the abnormality diagnosis terminal 131, and an output signal D is supplied toward another controller side (not shown in the figure).
FIG. 5 shows changes in voltage of the output signal C, the output signal D and a voltage of the grounding terminal 133 in the angular rate sensor, that occur when a circuit opens, for an instance, at a point xe2x80x9cXxe2x80x9d between the grounding terminal 133 of the driving circuit 134 and the earth ground.
In the prior art technique described above, it is possible to make a determination that an opening has taken place in the circuit, since the output signal D of the abnormality diagnosis terminal, 131 changes quickly from a high voltage level to a low voltage level as shown in FIG. 5, if the circuit opens at the point xe2x80x9cXxe2x80x9d between the grounding terminal 133 of the driving circuit 134 and the earth ground.
However, the output signal C of the sensor output terminal 129 shows a phenomenon, in which the voltage increases gradually toward a level of power source voltage E, as shown by a dashed line in FIG. 5, due to a combined impedance of the driving circuit 134 and the load resistors 136 and 137. Therefore, it is not possible to determine whether the angular rate sensor is normal or abnormal, with the output signal C alone.
In addition, a voltage of the grounding terminal 133 shows only a phenomenon of increasing gradually to the level of power source voltage E, it is not possible to distinguish between normality and abnormality of the sensor with this signal.
However, there are controllers, depending on their types, that are not capable of taking an output signal D of the abnormality diagnosis terminal 131 due to a limitation in number of input signals. Or, there are other cases wherein a system distributes and inputs only an output signal C of the sensor output terminal 129 into a plurality of controllers to serve for their individual control functions. It is desirable for a system of these types to instantly determine whether the angular rate sensor is normal or abnormal, only with the output signal C of the sensor output terminal 129.
The angular rate sensor of the present invention comprises:
(a) a vibration exciter for providing a vibration body with vibrations;
(b) a means for detecting a level of vibrations of the vibration body;
(c) a detecting means for detecting a Coriolis"" force produced in proportion to an angular rate;
(d) a current amplifier for amplifying an output signal of the means of detecting a level of vibrations;
(e) a full-wave rectifier circuit for producing a D.C. voltage by rectifying an output signal of a band-pass filter, wherein an output signal of the current amplifier is input;
(f) an automatic gain control circuit whose amplification factor for the output signal of the band-pass filter varies according to a magnitude of an output signal of the full-wave rectifier circuit;
(g) a driver for driving the vibration exciter according to a magnitude of an output signal of the automatic gain control circuit;
(h) a charge amplifier for inputting and amplifying a signal detected by the detecting means for detecting a Coriolis"" force;
(i) a synchronous detection circuit for detecting an output signal of a bandpass filter, wherein an output signal of the charge amplifier is input;
(j) a sensor output terminal for outputting an output signal of a low-pass filter, wherein an output signal of the synchronous detection circuit is input;
(k) a determination circuit for inputting the output signal of the full-wave rectifier circuit and the output signal after amplified by the charge amplifier, and for determining an abnormality; and
(l) an output clamping circuit activated by an output signal of the determination circuit, when the determination circuit makes a determination of abnormality, for clamping the output signal of the sensor output terminal at a level close to a power supply voltage or a grounding voltage. This structure can realize the angular rate sensor that is capable of making a determination instantly only with a sensor output signal, as to whether the angular rate sensor is normal or abnormal.